A silicon steel sheet having excellent magnetic properties is widely used as a material for, for example, iron cores of transformers and motors. In addition, from the viewpoint of magnetic property (iron loss), it is preferable that a high-silicon steel sheet be used because the iron loss of a silicon steel sheet decreases with an increase in Si content.
Since the toughness of steel decreases with an increase in Si content, it is difficult to manufacture a thin steel sheet by using a commonly used rolling method. However, since a method of manufacturing a high-silicon steel sheet having a silicon content of about 6.5 mass % by using a gas-phase siliconizing method has been developed, mass production of a high-silicon steel sheet is possible on an industrial scale nowadays.
When a high-silicon steel sheet is used as parts of, for example, transformers and motors, it is necessary to perform punching work. However, since cracking tends to occur due to the brittleness of a high-silicon steel sheet, when punching work is performed, it is necessary to perform punching work in a warm temperature range, as stated in Japanese Unexamined Patent Application Publication No. 62-263827, or under a strictly controlled processing condition regarding, for example, mold clearance.
However, to perform warm working, it is necessary to use a pressing machine having a heating device, and an expensive high-precision mold is indispensable because it is necessary to design a mold in consideration of thermal expansion.
In addition, although it is possible to perform punching work at room temperature if clearance is controlled to be much smaller than that in an ordinary electrical steel sheet, there is a problem in that, for example, chipping tends to occur due to severe wear damage on the mold in this case. In addition, since clearance increases with an increase in the number of punching operations, there is a problem of an increase in the frequency of changing a mold.
It could therefore be helpful to provide a high-silicon steel sheet excellent in terms of punching workability and magnetic property.